Clinical applications of ultrasonic imaging are expanding as the operating frequency increases. Some new applications require frequencies higher than 30 MHz emerge, such as opthalmological and dermatologicial imaging, as well as intravascular imaging with probes mounted on catheter tips. High frequency ultrasonic transducer (HFUT) has thus been a growing research area in recent years. With the operating frequency increasing, however, conventional transducer machining techniques are facing more and more difficulties in handling the miniaturized element and inter-element dimensions. Piezoelectric micromachined ultrasonic transducers (pMUTs) have thus been investigated as a promising new approach. By employing the well-established MEMS technologies, pMUTs offer advantages such as size miniaturization, parallel processing, batch production with high precision, repeatability and yield, and low cost and possible realization of complete systems-on-a-chip.
Most of the piezoelectric MEMS devices reported are using piezoelectric PZT ceramic films, ZnO films, or PVDF films as the functional materials. The relaxor-based piezoelectric single crystal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT), although possessing extraordinary piezoelectric properties, are rarely reported being used for this purpose because it is difficult to grow single crystalline PMN-PT thick films directly on silicon wafers.
It is an object of the present invention to combine a piezoelectric wafer and a silicon wafer through bonding and thinning the piezoelectric wafer.